Capacitive-discharge ignition system



March 17, 1970 G. v. ILINSK! CAPACITIVE-DISCHARGE IGNITION SYSTEM Filed Nov. 28, 1967 r! 3 f n] w e M w 0 United States Patent US. Cl. 123-448 4 Claims ABSTRACT OF THE DISCLOSURE A capacitor discharge ignition system for automotive internal combustion engines which includes and utilizes conventional low voltage D-C power source, coil, distributor, breaker points and spark plugs, said system including a step-up D-C to D-C converter connected with the power source, a saturable capacitor connected between the power source and coil, circuit means to effect discharge of the capacitor and including a silicon controlled rectifier, the gate of which is directly grounded and the anode of which is connected between the converter and capacitor and triggering means to intermittently open and close the rectifier and including a circuit connected with and between the power source, breaker points and rectifier cathode and adapted to apply negative voltage to the cathode with respect to the gate and such that the voltage between the breaker points does not exceed the voltage of the power source and the potential between the gate and cathode is below the maximum potential which the rectifier is capable of withstanding.

This invention relates to an ignition system for internal combustion engines and is more particularly concerned with an improved capacitor-discharge ignition system for such engines.

The ordinary or conventional ignition system for internal combustion engines includes a primary low voltage circuit and a secondary high voltage circuit.

The primary circuit includes a source of low voltage direct current, such as a battery, a primary winding of a step-up transformer, commonly referred to as a coil, a power line between and connected with the battery and one terminal of the winding, and mechanical switching means commonly referred to as breaker points interposed in the power line and driven by the engine to open and close the circuit in predetermined timed relationship with the engine.

The secondary high voltage circuit includes a secondary winding in the coil and inductively coupled with the primary winding, a distributor which is in the nature of a mechanical switching means driven by the engine in predetermined timed relationship with the engine and connected with the secondary winding and operable to sequentially direct high voltage discharges from the coil to spark plugs related to the several cylinders of the engine.

In such a system the points are closed to effect the building up of a magnetic field in the coil. When the desired field is established the points are opened which results in a ra id collapse of a magnetic field and a resulting induced high voltage surge of current in the secondary winding. The surge of high voltage current induced in the secondary winding, each time the magnetic field collapses, is directed to a predetermined spark plug of the engine by the distributor.

Such systems leave much to be desired. The many shortcomings of such systems are so well known to those skilled in and familiar with the .art that detailed consideration thereof can be dispensed with.

A capacitive-discharge ignition system distinguishes from the above-noted conventional system in that the desired surges of high voltage current for distribution to the spark plugs by the distributor are induced in the secondary winding of the coil by rapid build-up of the magnetic field in the coil rather than by the collapse of the said field. This is accomplished by providing a high voltage power source for the primary circuit of the system, providing a capacitor in the power line to the coil and providing suitable control means for discharging the capacitor in synchronism with the engine, as required.

Capacitive discharge ignition systems have long been recognized as the most desirable systems since the operating frequency of such systems can be increased to extremely high values, greatly increasing the ability of the system to fire the spark plugs. Such a system will properly and dependably fire spark plugs in high compression engines operating at high r.p.m. and where conventional systems will fail. Further, it will fire plugs, under such conditions which plugs would be considered fouled and unsuitable for use in connection with a conventional ignition system under any operating conditions.

The necessary source of high direct current voltage for capacitive discharge ignition systems can be and is easily and conveniently obtained through the use of a DC-DC converter of suitable design connected with and receiving current from a conventional storage battery.

To date, capacitive discharge ignition systems have been extremely complicated and costly, the control means therefor taking many special and unique forms.

Since the voltage for the primary coil winding in capacitive discharge systems must be considerably higher than in conventional inductive discharge ignition systems, for example, two or three hundred volts as compared with twelve volts, conventional breaker points and similar mechanical switching means cannot be employed as the high voltage primary current jumps or arcs between the contacts of such means and results in inoperability or their early and rapid breakdown and deterioration. This had lead the prior art to develop and employ complicated, extremely costly and not too dependable electronic means employing transistors and other exotic electrical components to take the place of the known mechanical switching means that would, but for the high voltage, be suitable.

An object of this invention is to provide a capacitive discharge ignition system for internal combustion engines which is extremely simple, highly effective and dependable in operation.

It is an object and feature of the invention to provide such a system in which discharge of the capacitor is controlled by a single silicon controlled rectifier which 1s controlled by a novel, extremely low voltage triggering mode.

Yet another object of the present invention is to provide a novel triggering mode that can be advantageously related to and controlled by a standard or conventional breaker point mechanism.

It is an object of the present invention to provide a triggering mode for a silicon controlled rectifier in a system of the character herein concerned with wherein the gate of the rectifier is grounded and the rectifier is triggered on by a negative voltage applied to the cathode, thereby allowing a static olf bias of the rectifier without having a negative power supply available.

The various objects and features of my invention will be fully understood from the following detailed description of typical preferred forms and applications of the invention, throughout which description reference is made to the diagrammatic accompanying drawings.

Referring to the drawings, the capacitive discharge ignition system that I provide includes, generally, an internal combustion engine E with a plurality of spark plugs S related to and adapted to ignite a fuel-air mixture in the cylinders of the engine (not shown), a source of electrical energy such as a storage battery B, a high voltage circuit H and a low voltage circuit L. The high voltage circuit includes the secondary winding W of a step-up transformer or ignition coil C, which is common to both circuits H and L, a distributor D in the form of a rotary switch driven in synchronism with the engine E and adapted to receive current from the winding W and to distribute it sequentially to the several spark plugs. The low voltage circuit includes the primary winding W of the ignition coil C, a power supply P in the form of a DC-DC converter adapted to step up the voltage of the battery B to a magnitude of 300 to 400 volts, as desired or as circumstances require.

The circuit L further includes a power line between and connecting the power supply P with the primary coil winding W, and a capacitor R in the line 10.

The system further includes a low voltage triggering circuit T, which circuit is adapted to effect discharge of the capacitor R in timed relationship with the engine E whereby current flow is initiated through the primary winding W of the ignition coil C each time a spark plug is to be fired, which current flow builds a magnetic field in the ignition coil and induces the desired high voltage current flow in the secondary winding \V' of the coil.

The circuit T includes, generally, a mechanical automotive-type breaker points mechanism driven synchronously with the engine E and the distributor D and connected with the battery B, a silicon controlled rectifier S with its anode connected to the line 10 between the capacitor R and the power supply P, and a novel trigger mode for the rectifier S and connected with the cathode of the rectifier S and under control of the breaker points The coil C is a standard or conventional automotive ignition coil. The high voltage circuit H of my system, which includes the secondary winding W of the coil C, is a standard or conventional high voltage or secondary ignition circuit. The distributor D is a conventional or standard automotive distributor construction, familiar to all those skilled in the art and includes a plurality of circumferentially spaced spark contacts 11, each of which is connected with the spark plugs S of the engine E by a high tension spark plug line 12, a rotary contact arm 13 carried by a distributor shaft 14, which shaft is coupled with and driven by the engine E in timed relationship therewith. The contact arm 12 is connected with the positive terminal of the secondary winding W of the coil C by a high tension coil line 15 and is adapted to conduct high voltage current, sequentially from the several spark plugs S.

The power supply P of the primary or low voltage circuit L of the system that I provide serves to increase the low voltage direct current from the battery B (12 volts) to a relatively high voltage direct current, for example 300 volts.

'In the case illustrated the power supply P is a transistorized DC-DC converter and includes a step-up transformer having a core 21, a first primary winding 22, and a secondary winding 23. The primary winding 22 is grounded at its center as at 24 and its opposite ends are suitably connected with the collectors 25 of a pair of transistors 26 and 26. The bases 27 of the transistor 26 and 26' are connected wtih related ends of second primary windings 28 and 28. The other or unrelated ends of the second primary windings 28 and 28' are connected with one, common end of a resistor 29 by lines 30 and 30', respectively. The other end of the resistor 29 is connected with the battery B by means of a power line 31.

The emitters 32 of the transistors 26 and 26 are connected with the power line by lines 33 and 33, respectively.

In addition to the foregoing, the line 30 is connected with ground by a line 34 in which a resistor 35 is engaged. A suitable capacitor 36 is connected between the ground end of the resistor 35 and the line 30 between the second primary winding 28 and the line 34.

The. opposite ends of the secondary winding 23 of the transformer 20 are connected with opposite legs of a full Wave rectifier bridge 40. One leg 41 of the bridge 40 is connected with the line 10 and is, therefore, connected directly with one side (the left side) of the capacitor R. The leg 41 is provided with a diode 42 allowing for current flow from right to left and towards the winding 23.

Another leg 43, with a diode 44 allowing for current fiow from left to right and from the winding 23 is connected with the other end of the winding 23. The other end of the line 43 connects with a ground line 45 and with a conductor line 46 extending to and connected with the lower, positive end of the primary Winding W and lower negative end of the secondary winding W of the coil C.

The bridge further includes a third leg 47 between the leg 41 at the coil side of the diode 42 and the leg 43 at the side of the diode 44 remote from the coil 23 and having a diode 48 allowing for current flow from the leg 41 to leg 43 only and a fourth leg 49 between the leg 41 at the side of the diode 42 remote from the winding 23 and the leg 43 between the diode 44 and the coil 23 and having a diode 50 allowing for current fiow from the leg 41 to the leg 43 only.

The silicon controlled rectifier S has its anode 51 connected with the line 10 between the bridge 40 and rectifier R by a line 52, its gate 53 being grounded as at 54. The cathode 55 of the rectifier S is connected to ground as at 56 by a line 57 in which is arranged a diode. 58 which allows for current flow from ground only.

The triggering circuit, in addition to the grounds 54 and 55, line 57 and diode 58, includes a ground 60 connected with one contact 61 of the breaker points P, a conductor line 63 from the other contact 63 of the breaker points P to the battery B, a resistor 64 in the line 62, a transistor 65, a line 66 between the base 67 of the transistor and the line 62 at the ground end of the resistor 64 and a resistor 68 in the line 66, a line 69 from the emitter 70 of the transistor 65 to ground, as at 70, a resistor 71 in the line 69, a conductor line 72 between the collector 73 and the line 57 and connected with the line 57 between the rectifier S and the diode 58, a capacitor 75 in the 72, a line 76 between the battery and a capacitor 75, between the rectifier S and the connection between the lines 57 and 72, a resistor 77 in the line 76 and a coupler line 78 with a resistor 79 connected between the lines 72 and 76, between the transistor 65 and capacitor 75 and between the resistor 77 and battery B.

In addition to the foregoing, the system is shown provided with a resistor 80 connected between the line 52 and the line 10, between the capacitor R and the coil C and a capacitor 81 with one side grounded as at 82 and its other side connected with the line 52 between the rectifier S and the point of connection with the resistor 80.

In operation, and referring first to the DC-DC converter P, it is to be noted that the transistors 26 and 26 are not exactly matched and that one will conduct first or before the other.

Assuming that the transistor 26 is the first to conduct, electron flow will be from ground at 24, through the primary winding 22 of the step-up transformer 20, through the collector 25 and emitter 32 of the transistor 26, through line 33 to the positive side of the power source or battery B, which, for example, is 12.6 volts.

This above process is regenerative in transistor 26 because of the base drive polarity at 27 and is degenerative in transistor 26 because of the base drive polarity at 27'.

When the core 21 of the transformer 20 becomes saturated, the process set forth above reverses, shutting transistor 26 off and turning transistor 26 on, whereupon current flows from ground 24 through the primary winding 22 of the transformer 20, through collector 25 and emiter 32 of transistor 26, then through line 33' to the battery B.

The transformer 20 is a step-up transformer and supplies high voltage alternating current to the rectifier 40 of the converter.

The rectifier 40 comprising the lines 41, 43, 47 and 49 and the diodes 42, 44, 48 ad 50 is a full Wave bridge rectifier and supplies positive high voltage direct current to the capacitor R, at the left side thereof and to the anode 51 of the silicon controlled rectifier S.

When the capacitor S is fully charged with a positive voltage on the left side and the points, that is, the contacts 61 and 63 of the breaker points mechanism P are closed, the base 67 of transistor 65 being grounded at 60, through the proints, through -the lines 62 and 66 and through the resistor 68 in line 66, is at the same potential as the emitter 69, grounded at 70 through resistor 71. This turns transistor 65 off.

With transistor 65 turned off and non-conductive, capacitor 75 in line 72 and connected between the line 57 and the collector 73 of transistor 65 will charge up with a positive charge at its left side as a result of current flow from ground 56, through. diode 58 and from the left side of the capacitor 75 through line 72, line 78 and resistor 79 and thence to the battery B through line 76. (1 ms. time constant for point bounce protection for false firing.) At the same time current flows from ground 56 through diodes 58 and resistor 77. This flow establishes an ofl? bias for the gate 53 and cathode 55 of the silicon controlled rectifier. The grounded gate 53 and the cathode 55 of the silicon controlled rectifier being in parallel with diode 58, the current flow through diode 58 establishes or applies a positive off bias between the gate and cathode and the rectifier S is turned off and rendered more non-conductive than zero bias would allow.

When the points P open, an on bias path is established for transistor 65, from ground at 70 through resistor 71, emitter 69 to base 67, resistor 68, resistor 64 and thence to battery B. The transistor being thus turned on, the left side of capacitor 75 is grounded through transistor 65 and resistor 71.

Capacitor 75 being charged with 12 volts when the points are closed and with the left. side thereof grounded as set forth above, the right side of the capacitor 75 goes negative. This negative voltage is applied to the cathode 55 of the silicon controlled rectifier S. Since the gate 53 of rectifier S is grounded, the negative voltage applied to the cathode turns rectifier S on and the capacitor discharges through the cathode-gate of rectifier S.

It is to be noted that using a negative voltage generated in the above manner to trigger a silicon controlled rectifier cathode, with the gate grounded, allowing a static off bias for the rectifier and without having a negative power supply available is highly unique.

When the silicon controlled rectifier S turns on, capacitor R discharges through line to and through the primary winding W of the coil C, current flow being from ground '56, diode 58 and through rectifier S.

Also, when the rectifier S turns on as set forth above, the secondary winding 23 of the step-up transformer is shorted. The inverter action is stopped during the period that the rectifier S is turned on.

As the capacitor R discharge progresses, capacitor R will reach a zero voltage condition. However, current continues to flow in the same direction because of the continued collapsing of the magnetic flux in the coil C.

When the flux in coil C has fully collapsed capacitor R is charged up with a negative voltage on the left side. At this time, the silicon controlled rectifier S turns off and the diode bridge is turned on by this negative voltage,

allowing capacitor R to discharge from the left side through the diodes, up through the primary winding W of the coil to the right side of the capacitor R.

Again, flux is built up in the coil as capacitor R discharges.

When capacitor R again reaches zero voltage, continued collapsing of the magnetic flux in the coil C maintains the current flow through the diode bridge of the inverter section and charges the capacitor R with a plus voltage on the left side, thereby recovering unused energy.

When the magnetic flux is again fully collapsed, the diodes of the bridge turn off, removing the short across the secondary winding 23 of the step-up transformer 20 allowing the inverter to restart, which then completes the charge on capacitor R.

After this time, points P close and the process is readied for recycling.

The speed or [rapidity at which the inverter restarts is a function of resistors 29 and 35.

Capacitor 36 acts as a filter across resistor 35 to minimize secondary breakdown of transistors 26 and 26'.

Having described only a typical preferred form and application of my invention, I do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to myself any modification and/or variations that may appear to those skileld in the art.

I claim:

1. An ignition circuit for an internal combustion engine comprising an ignition coil having a primary winding and a secondary winding, spark discharge means connected across said secondary winding, engine driven switching means, a direct current voltage source, a step-up D-C to D-C converter connected with the voltage source and with the ends of the primary winding, a saturable capacitor between and connected with said converter and one end of the primary winding, means to discharge said capacitor and including a silicon controlled rectifier having an anode a cathode and a gate, said gate connected with ground, said anode connected with the side of the capacitor remote from the coil and triggering means comprising a circuit connected with and between the cathode, switching means and said voltage source to intermittently apply negative voltage to the cathode with respect to the gate to turn the rectifier on and effect discharge of the capacitor.

2. A circuit as set forth in claim 1 wherein said switching means has one contact connected to ground and another contact connected with the power source through a second line, a first resistor in said second line, a first line from the cathode to grotmd, a diode in said first line conducting from ground, a second capacitor with one side connected with said first line a transistor having a collector connected with the other side of the second capacitor, an emitter connected with a second resistor and thence to ground, a base connected with a third resistor and thence to the second line at the ground end of the first resistor, a fourth resistor connected between the power source and the first line between the cathode and the second capacitor and a fifth resistor between the power source side of the fourth resistor and said other side of the second capacitor, said transistor being non-conductive, the second capacitor charging up and the silicon controlled rectifier being turned off by a static 01f bias and non-conductive when the contacts are closed, said transistor being conductive to ground when said switching means is open, said other side of the second capacitor to discharge s-aid capacitor and direct a negative voltage to said cathode to turn the rectifier on, grounding the firstm-entioned capacitor through the rectifier and effecting discharge thereof.

3. An ignition system including a low voltage direct current power source, a step-up induction coil with primary and secondary windings, a plurality of spark plugs, a distributor between the plugs and the secondary winding to sequentially conduct high voltage discharge from the coil to the severalspark plugs, a breaker point mechanism, means synchronously driving the distributor and breaker point mechanism with a related internal combustion engine, a transistorized DC-DC converter including a low voltage section connected with the power source, a step-up transformer and a high voltage section with a rectifier bridge to deliver high voltage direct current, a first capacitor between and connected with one leg of the bridge and one end of the primary winding, the other end of the primary winding connected with another leg of the bridge, a silicon controlled rectifier with its gate grounded and its anode connected between the first capacitor and the leg of the bridge connected with said first capacitor, a triggering section to turn the silicon controlled rectifier off and on and efiect discharge of the capacitor and including a first line between the cathode of the silicon controlled rectifier and ground, a ground to one side of the breaker point mechanism, a second line from the other side of the breaker point mechanism to the power source, a second capacitor with one side connected with the first line, a transistor with its emitter grounded, its collector connected with the other side of the second capacitor and its base connected with the second line, a third line between the power source and the first line between the silicon controlled rectifier and second rectifier, a first resistor in the third line, and a second resistor between the power source side of the first resistor and the transistor side of the second rectifier whereby the base and emitter are at the same potential and the transistor is turned off when the breaker points mechanism is closed and the second capacitor charges up, a current path through the third line establishes a negative off bias at the cathode of the silicon controlled rectifier and whereby the transistor is turned on when the breaker points mechanism opens, the second capacitor is grounded through the transistor and discharges to change polarity and apply a negative voltage at the cathode of the silicon controlled rectifier, turning said rectifier on to ground and effect discharge of the first capacitor.

4. A circuit as set forth in claim 1 wherein said switch ing means has one contact connected to ground and another contact connected with the power source through a second line, a first resistor in said second line, a first line from the cathode to ground, a diode in said first line conducting from ground, a second capacitor with one side connected with said first line, a transistor having a collector connected with the other side of the second capacitor, an emitter connected with a second resistor and thence to ground, a base connected with a third resistor and thence to the second line at the ground side of the first resistor, a fourth resistor connected between the power source and the first line between the cathode and the second capacitor and a fifth resistor between the power source side of the fourth resistor and said other side of the second capacitor, said transistor being nonconductive, the second capacitor charging up and the silicon controlled rectifier being turned off by a static otf bias and non-conductive when the contacts are closed, said transistor being conductive to ground, said other side of the second capacitor to discharge said capacitor and direct a negative voltage to said cathode to turn the rectifier on, grounding the first-mentioned capacitor through the rectifier and effecting discharge thereof, said switching means comprising a conventional breaker points mechanism.

References Cited UNITED STATES PATENTS 3,342,167 9/l967 Tarter 123-148 3,357,415 12/1967 Huntzinger 123-148 3,381,172 4/1968 Weiner 315-212 LAURENCE M. GOODRIDGE, Primary Examiner U.S. Cl. X.R. 3l5209 

